Arterial hypertension affects over 50 million Americans. While drug treatment is effective, exercise would be safer, might be cheaper, and would bring added health benefits if it could replace drugs in controlling hypertension. The aims of this study are to: 1) determine if two 18 month long endurance training programs, one of high intensity and one of moderate intensity, can replace medication as a treatment for mild essential hypertension, 2) determine if a moderate intensity endurance training program is as effective as or more effective than a high intensity program in allowing mild essential hypertensives to discontinue anti-hypertensive medication, 3) determine if physiological, psychological, and compliance variables predict success in allowing mild essential hypertensives to discontinue anti-hypertensive medication. The investigators propose a randomized controlled trial. Known hypertensives (n=162) whose diastolic blood pressures rises to between 90 and 104 within four months of discontinuing medication under careful observation will have their pressures controlled with enalapril. Half the subjects will be female and half male, and their racial characteristics will generally reflect that of our managed care population (about 20% black). V02 peak will be measured during cycle ergometry. Eligible subjects will be randomly assigned to 18 months participation in one of three groups: 1) high intensity endurance training (35 minutes 3 times/week at heart rate at 70-85% of V02 peak), 2) moderate intensity endurance training (35 minutes 3 times/week at heart rate of 50-70 of V02 peak), and 3) contact control. Enalapril will be forward or back titrated or discontinued to maintain a normal blood pressure. After 12 months participation, medication will be withdrawn under careful supervision from all subjects still taking it. They will test the hypotheses that: 1) a greater number of subjects undergoing either or both of the two 18 month exercise training programs will be able to stop anti-hypertensive medication than non-exercising controls, 2) moderate and high intensity endurance training are equally effective in replacing drugs in the treatment of mild essential hypertension, and 3) subjects that are successful at withdrawing anti-hypertensive medication will have: greater improvements in V02 peak, better initial psychological status or greater improvements in psychological status, and greater compliance with the exercise training program. The investigators state that this study will be a critical test of whether endurance training can replace medication in an important number of patients as a treatment for hypertension.